Comment by avianlyric

Sure everyone these day maps their local references back to WGS84, but the local references are still tied to local datum.

Plate tectonics can result in some parts of the world moving at up 10cm a year, which over 10s to 100s of years can add up to something pretty significant. Funnily enough an OSM April Fools joke is a good place to learn more[1].

Talking of the UK. Ordinance survey still maintain their own master geodesics, and geographic references, which allows them to tie the OS grid (which what the land registry uses to locate property) back to WGS84, as both WGS84 and the UK slowly drift around due to various reasons (such as improved tech to refine the definition of WGS84, tectonic drift etc). You joke about the ice age and glaciers, but the UK is still “recovering” from all that ice, resulting in vertical movement of about 1m every 100 years. Which given how long property rights can last (Oxford University is almost 1000 years old), can actually turn into a material difference, and real land disputes, over time, if not properly corrected for.

Each of these adjustments may seem insignificant on their own, but they accumulate over time, and it gets complicated when these adjustments are forced to interact with humans, our somewhat fuzzy perception of reality, and general disregard for well defined coordinate systems which don’t align well with our “intuitive” understanding of the world.

None of this is any different to how we deal with issues that are thrown up by our increasing ability to measure time accurately. We track International Atomic Time (IAT), which is time as tracked by a set of atomic clocks, but then we apply various adjustments to get UTC, which is human time. Those adjustments exists purely to keep UTC aligned to what humans expect, because the earths orbit wobbles enough that the absolute time produced by IAT doesn’t match up perfectly with how we’ve historically measured time. All of this seems a little silly, but we now live in a world where everyday systems depend on measures accurate enough that all this minor drift becomes important.